Anaesthetic delivery system

ABSTRACT

An anesthetic delivery system has a delivery unit containing a carbon dioxide retaining element and a reversible action anesthetic absorber/desorber for releasably retaining therein at least a portion of a charge of anesthetic agent. An externally accessible first internal flow section in the delivery unit directs gas through the delivery unit first through the anesthetic absorber/desorber and then through the carbon dioxide retaining element, sequentially. An externally accessible second internal flow section directs gas through the delivery unit via the anesthetic absorber/desorber and bypassing the carbon dioxide retaining element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an anesthetic delivery system and inparticular to a system adapted to re-use anesthetic that remainsunabsorbed by a patient from a previously inhaled anesthetic dose.

2. Description of the Prior Art

It is know from U.S. Pat. No. 4,015,599 to provide an anestheticdelivery system having a delivery unit that houses a carbon dioxideabsorber and a reversible action anesthetic adsorption filter arrangedin series and in gaseous communication with a gas flow passage thatprovides a flow path for gas through the unit via the carbon dioxideabsorber and the anesthetic adsorption filter. A charge of a gas-forminganesthetic is also provided as part of the system, pre-loaded into theanesthetic adsorption filter.

In use, the unit of the known anesthetic delivery system is disposed ingas flow connection with a tubing circuit of a so-called “closed”inhalation anesthesia system. The unit is intended to be used in amanner such that exhaled breathing gas within the tubing circuit passesfirst through the carbon dioxide absorber and then through theadsorption filter to collect. This anesthetic gas is then supplied intothe tubing circuit for inhalation by the patient, together with freshbreathing gas that is added after the unit to compensate for the gasthat was consumed.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an anesthetic deliverysystem adapted for use in a so-called “open” inhalation anesthesiasystem and which also allows the re-use of exhaled anesthetic.

This object is achieved in accordance with the present invention by ananesthetic delivery system having a delivery unit with two internal gasflow passages, an exhalation gas flow passage that conducts gas throughthe adsorption filter only, and an inhalation gas flow passage thatconducts gas through first the adsorption filter and then through thecarbon dioxide absorber. Thus any unused anesthetic in exhalation gas isretained by the filter and is returned (“reflected”), essentially freeof carbon dioxide, for re-inhalation by a patient while permitting themajority of exhaled carbon dioxide to pass through the unit. In thismanner the lifetime of the anesthetic charge may be extended withoutincreasing its size and the amount of carbon dioxide absorber materialmay be reduced compared to the known system, thereby enabling areduction in material costs and size of the delivery unit.

Usefully a bypass gas flow passage may be included within the unit andconfigured to provide a flow path for an amount, preferably a variableamount, of gas from the inhalation passage to bypass the anestheticfilter. In this manner take up of anesthetic may be controlled bycontrolling the gas flow through the anesthetic adsorption filter.

A variable flow restriction may be provided within either of the bypassgas flow passage and the inhalation gas flow passage to regulate theflow of gas in the inhalation line through the filter and therebyvariably control the concentration of anesthetic in the gas that passesout of the delivery unit. Usefully the variable flow restriction may beadapted to automatically regulate the flow of gas dependent on a sensedconcentration of anesthetic in the gas. Preferably a material, such assilicone rubber, that reacts to change its physical dimensions inresponse to an exposure to anesthetic, is employed in the variable flowrestriction. In this way sensing of the anesthetic concentration and thedependent control of the flow restriction may be carried out within thedelivery unit without the need of additional electronic sensor orcontrol arrangements.

The above object also in achieved in accordance with the presentinvention by an inhalation anesthetic system having a mechanicalbreathing aid which may be a ventilator or respirator of a stationarysystem or which may be, for example, a compressible bag or bottled gassupply, connectable to the airways of a patient by a gas flow circuithaving a common gas flow section in which inhalation gas from thebreathing aid can flow towards the patient and in which exhalation gasfrom the patient can flow towards the breathing aid. A delivery unit ofthe anesthetic delivery system is provided in fluid communication withthe flow circuit, preferably the common gas flow section, so thatinhalation gas can flow through the unit to receive a dose of theanesthetic agent held by the absorption filter and so that theexhalation gas can flow through the unit to deposit unused anestheticagent in the absorption filter together with a small amount of thecarbon dioxide present in the exhalation gas.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically a first embodiment of an anesthetic deliverysystem according to the present invention;

FIG. 2 is a schematic representation of an inhalation anesthetic systemaccording to the present invention.

FIG. 3 shows schematically a second embodiment of an anesthetic deliverysystem according to the present invention.

FIG. 4 shows part of a third embodiment of an anesthetic delivery systemaccording to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Considering now the anesthetic delivery system of FIG. 1, a deliveryunit 2 is, in the present embodiment, formed with ports 6 a, 6 b forproviding gas communication between internal and external the unit 2.Gas flow directions through the unit 2, when in use are shown, in FIG. 1by the arrows.

The port 6 a provides for gas communication between external the unit 2and a common flow passage 8 a internal the unit 2 whilst the port 6 bprovides for gas communication between external the unit 2 and a commonflow passage 8 b internal the unit 2. These common flow passages 8 a, 8b form part of both an inhalation gas flow passage (for gas flowingwithin the unit 2 from port 6 a, towards the port 6 b) and an exhalationgas flow passage (for gas flowing within the unit 2 from port 6 b,towards the port 6 a).

A reversible action anesthetic (adsorption/desorption) filter 10 formedof a suitable sorption material for anesthetic agent, such as zeolitesof crystalline aluminum silicates which may be pellets or supported on acarrier; an activated carbon filter such as formed fromcarbon-impregnated material, carbon fiber cloth, or granulated ormicroporous carbon material; or other microporous material, is arrangedin direct gas communication with the common flow passage 8 a. In thepresent embodiment this anesthetic sorption filter 10 is formed into tworegions. A first region 10 a is provided initially free of theanesthetic agent and a second region 10 b is pre-loaded with ananesthetic agent to be delivered to a patient. Optionally and asillustrated in the present embodiment, a first removable sealingmembrane 4 a, such as may be formed from an impermeable plasticsmaterial, is located between the first region 10 a and the second region10 b to act as a barrier for the transport of the pre-loaded anestheticagent into the second region 10 b. A second removable sealing membrane 4b is located to seal the second region 10 b against escape of anestheticagent from the filter 10. The two membranes 4 a, 4 b are removable fromthe filter 10 by pulling on externally accessible tab sections and areintended to be removed immediately before use of the unit 2. In thismanner the pre-loaded delivery unit 2 may be stored for extended periodswithout loss of anesthetic from the second region 10 b of the filter 10.

The filter 10 is located within the delivery unit 2 with the anestheticfree region 10 a relatively closer to the port 6 a and in fluidcommunication with the common flow passage 8 a. Pre-loading may beachieved in a number of ways, for example by passing an anestheticcontaining gas, in this embodiment preferably in a direction from theport 6 b to the port 6 a, through the unit 2 before any removablesealing membrane 4 a, 4 b is in place and until a required amount ofanesthetic agent has been retained by the anesthetic filter 10. This canbe monitored by monitoring the anesthetic concentration in gas exitingthe unit 2 through the port 6 a. Pre-loading of the filter 10 mayalternatively be carried out by passing an anesthetic containing gasthrough it before it is placed within the delivery unit 2.

A flow channel 12 is provided within the unit 2 for fluid communicationbetween the second region 10 b of the anesthetic filter 10 and a carbondioxide absorber 14. A one-way valve 16 is disposed relative to thecarbon dioxide absorber 14 to prevent gas flow into the absorber 14 fromthe port 6 b.

A bypass gas flow passage 18 is connected through an opening 20 with thecommon flow passage 8 a at a location between the port 6 a of the unit 2and the anesthetic filter 10.

A one-way valve 22 is provided to permit gas flow along the bypass gasflow passage 18 in a direction from the common flow passage 8 a only.The bypass gas flow passage 18 is arranged to provide a flow path forgas from the port 6 a to the port 6 b, avoiding the anesthetic sorptionfilter 10 and in the present embodiment terminates at an opening 24 inthe flow channel 12. A variable flow restriction 26 is provided incommunication with the bypass gas flow passage 18 and is movable to varythe resistance to gas flow within the bypass gas flow passage 18.

A flow passage 28 within the delivery unit 2 communicates with thecommon gas flow passage 8 b; with the second region 10 b of theanesthetic sorption filter 10 through the opening 24 in the flow channel12 and forms part of an exhalation gas flow passage. The flow passage 28is here shown to be provided with a one-way valve 30 to ensure gas flowthrough the passage 28 in one direction only—from the port 6 b towardsthe anesthetic filter 10, avoiding the carbon dioxide absorber 14.

An exemplary “open” inhalation anesthetic system 32 is shown in FIG. 2.A mechanical breathing aid 34, such as a ventilator, is shown in use ingas communication with the airways of a patient 36. The system 32 isprovided with a common gas line 38 for the delivery to and recovery fromthe airways of a patient 36 of anesthetic containing gases. Separateinhalation 40 and exhalation 42 gas lines are provided to connect thebreathing aid 34 with the common gas line 38.

The anesthetic delivery unit 2 of FIG. 1 is shown here as being seriesconnected to the common gas line 38 so that gas passing both to and fromthe patient will pass through the unit 2. The unit 2 is oriented withinthe common gas line 38 so that inhalation gas from the breathing aid 34will enter the unit 2 through the port 6 a and exhalation gas from theairways of the patient 36 will enter the unit 2 through the port 6 b. Tofacilitate this orientation a visible indication, such as an arrow 44showing the intended direction of gas flow through the unit 2 towardsthe patient 36, may be provided on an external surface of the unit 2.

In use the delivery unit 2 is intended to receive inhalation gas forinhalation by a patient 36 through the port 6 a and into the common gasflow passage 8 a. This inhalation gas may then be divided to flow partlythrough the anesthetic filter 10 and partly through the bypass gas flowpassage 18 to avoid the filter 10. The gas flowing through the filter 10picks up anesthetic agent together with carbon dioxide that may bepresent within the filter 10 and flows towards the carbon dioxideabsorber 14. It will be appreciated that by moving the flow restriction26 to alter the resistance to flow it presents then the amount ofinhalation gas flowing through the absorption filter 10 can be variedand the concentration of anesthetic in the inhalation gas that exits theunit 2 through the port 6 b controlled.

In the present example this anesthetic containing inhalation gas isrecombined with the inhalation gas from the bypass gas flow passage 18in the flow channel 12 before it passes through the carbon dioxideabsorber 14. Carbon dioxide that was picked up by the inhalation gas asit passed through the anesthetic filter 10 will be captured by thecarbon dioxide absorber 14. The essentially carbon dioxide freeinhalation gas then flows through the one-way valve 16, along the commonflow passage 8 b and out of the delivery unit 2 through the port 6 bcarrying with it a dose of anesthetic for inhalation by the patient 36.

Exhalation gas from the patient 36 will typically contain carbon dioxideand an amount of unused anesthetic. In use the delivery unit 2 isintended to receive this exhalation gas through the port 6 b and in tothe common flow passage 8 b. The combination of one-way valves 16, 22,30 ensures that exhalation gas flows only through the exhalation flowpassage 28, via the gas flow channel 12, and into the anesthetic filter10, avoiding the carbon dioxide absorber 14. As the exhalation gaspasses through the filter 10 any unused anesthetic in the gas will beretained together with a small amount of the carbon dioxide that willalso be present in the exhalation gas. The substantially anesthetic freeexhalation gas then flows into the common flow passage 8 a and out ofthe unit 2 through the port 6 a. In this manner the effectiveness of thedelivery unit 2 in delivering anesthetic doses is prolonged since theanesthetic charge that was initially loaded into the sorption filter 10is partially restored with unused anesthetic present in the exhalationgas that the delivery unit 2 “reflects” back to the patient's airways36.

A second embodiment of an anesthetic delivery system is shown in FIG. 3.A delivery unit 46 is configured with gas flow paths substantiallysimilar to those illustrated in FIG. 1 and are again shown by arrows inthe present figure. For ease of understanding items of the unit 46 ofFIG. 3 that are substantially similar to items of the unit 2 of FIG. 1are identified with corresponding reference numerals.

As described with respect to FIG. 1, a port 6 a is provided in the unit46 and delimits one end of a common flow passage 8 a. An anestheticfilter 48 is located with a first side in gas communication with thecommon flow passage 8 a and with a second, opposing, side for gascommunication with a removable carbon dioxide filter 50 by means of aflow channel 12. The carbon dioxide filter 50, when inserted into theunit 46 (broken line construction of FIG. 2) through the co-operatingaccess slot 52, is also located in gas communication with a secondcommon flow passage 8 b that is delimited at one end by a port 6 b inthe unit 46. A one-way valve 16 is disposed to prevent gas flow from thecommon flow passage 8 b into the carbon dioxide filter 50.

The common flow passage 8 b also provides for gas communication betweenthe port 6 b and a flow passage 28 that is arranged to communicate withthe anesthetic filter 48 via an opening 24 in the common flow passage12. A one-way valve 30 ensures that gas can only flow in the flowpassage 28 in a direction from the port 6 b.

Different from the embodiment of FIG. 1, a bacteria filter 54 islocated, optionally removably located, in the flow passage 28 to preventcontamination of the anesthetic filter 48 by bacteria that may bepresent in exhalation gas flowing into the unit 46 through the port 6 b.

Also different from the embodiment of FIG. 1, the delivery unit 46 ofFIG. 3 contains a housing 56 in which is held a charge 58 of anestheticagent within a frangible container 60. The housing 56 is provided withan opening 62 through which the charge 58 of anesthetic agent may flowto load the anesthetic filter 48 prior to use. The housing 56 is herealso provided with internal walls 64, shaped to funnel the flow ofanesthetic agent towards the opening 62. The housing 56 is furtherprovided with an inwardly deformable wall section 66 that is accessiblefrom external the delivery unit 46. In use, an external force may beapplied to this wall section 66 to cause its deformation and aconsequent transmission of the force to the frangible container 60. Thisresults in the container 60 breaking to release the charge 58. Aremovable rigid cover 68 is preferably provided to overlay thedeformable wall section 66 to prevent accidental breakage of thecontainer 60. The housing 56 and the anesthetic filter 48 may be formedas a single unit, so as to be removable, within the delivery unit 46.

A bypass gas flow passage 18 is connected for fluid communication withthe common flow passage 8 a by an opening 20 and with the carbon dioxidefilter 50 through the opening 24 in the flow passage 12. Similar to theembodiment of FIG. 1, a one-way valve 22 is provided to ensure that gasis able to flow through the bypass gas flow passage 18 only in thedirection from the common flow passage 8 a, towards the carbon dioxidefilter 50. A vane 70 is provided within the passage 18 and is rotatableto present a variable resistance to gas flow from the common flowpassage 8 a and thereby control the amount of gas bypassing theanesthetic filter 48. The vane 70 is coupled to an anestheticconcentration sensor 72 via a linkage 74. The rotational position of thevane 70 is automatically variable to change the flow resistance itpresents dependent on the concentration of anesthetic that is sensed bythe sensor 72. In the present exemplary embodiment the concentrationsensor 72 is formed of a silicone rubber block, a material that variesits physical dimensions in response to exposure to anesthetic,configured such that, in co-operation with the linkage 74, it will exerta force on the vane 70 tending to cause the vane 70 to rotate andpresent a reducing resistance with increasing anesthetic concentrationat the sensor 72.

A part of third embodiment of an anesthetic delivery system according tothe present invention is shown in FIG. 4 and shows an anestheticabsorption filter arrangement that may be employed as an alternative tothose of FIG. 1 and FIG. 2. In this third embodiment a membrane 76replaces part of an external wall 78 of an anesthetic delivery unit 80.The membrane 76 is of a type well known in the art of, for exampleimplantable insulin pumps or of drug administration in ventilators, andis formed of a material that re-seals when a puncturing syringe needleis withdrawn. The membrane 76 of the present embodiment partiallyoverlays and is presented here as being in intimate contact with anouter surface 82 of an anesthetic sorption filter 84. A charge 86 ofanesthetic agent is provided in a syringe 88 for injection through themembrane 76 and into an anesthetic receiving portion 84 b of the filter84 to load at least part of the filter 84 with anesthetic agent fordelivery to a patient. In this manner a region 84 a of the anestheticfilter 84, which corresponds to that region 10 a of the filter 10 of theembodiment shown in FIG. 1, may be provided that is initiallysubstantially anesthetic free.

It will be appreciated that by using the combination of re-sealablemembrane 76 and syringe 88 the sorption filter 84 may be optionallyre-loaded during use. Moreover, this combination enables the filter 84to be loaded immediately before use, which facilitates the storage ofthe anesthetic delivery system. Additionally the filter 84 may be loadedwith an anesthetic agent of choice so that only a single constructiontype of delivery unit 80 needs to be manufactured.

Although modifications and changes may be suggested by those skilled inthe art, it is the invention of the inventors to embody within thepatent warranted heron all changes and modifications as reasonably andproperly come within the scope of their contribution to the art.

1. An anesthetic delivery system comprising: a delivery unit containingan anesthetic absorber/desorber and a carbon dioxide retaining element;an externally accessible first internal flow section in said deliveryunit directing gas sequentially first through said anestheticabsorber/desorber and subsequently through said carbon dioxide retainingelement; an externally accessible second internal flow section in saiddelivery unit directing gas through said delivery unit through saidanesthetic absorber/desorber and bypassing said carbon dioxide retainingelement; and a third internal flow section in said delivery unit ingaseous communication with said first internal flow section andconfigured to provide a flowpath for only a portion of gas from saidfirst internal flow section to said carbon dioxide retaining element andsaid portion bypassing said anesthetic absorber/desorber.
 2. Ananesthetic delivery system as claimed in claim 1 comprising a source fora charge of anesthetic agent, in gaseous communication with saidanesthetic absorber/desorber, for releasable retention by saidanesthetic absorber/desorber.
 3. An anesthetic delivery system asclaimed in claim 1 comprising a flow divider in said delivery unitoperable to vary a relative proportion of gas flow between said firstinternal flow section and said third internal flow section.
 4. Ananesthetic delivery system as claimed in claim 3 wherein said flowdivider comprises a variable flow restriction presenting a variableresistance to gas flow.
 5. An anesthetic delivery system as claimed inclaim 4 comprising an anesthetic concentration sensor disposed in saiddelivery unit at a location to sense a concentration of anesthetic ingas in said first internal flow section downstream of said anestheticabsorber/desorber, said anesthetic concentration sensor being operablyconnected to said variable flow restriction for automatically changingsaid relative proportion dependent on said concentration of anesthetic.6. An anesthetic delivery system as claimed in claim 5 wherein saidanesthetic concentration sensor comprises a material having physicaldimensions that change dependent on a level of exposure to saidanesthetic, and comprising a mechanical linkage operably connecting saidmaterial to said variable flow restriction and moving said flowrestriction dependent on said change in said physical dimensions to varysaid relative proportion.
 7. An anesthetic delivery system as claimed inclaim 1 wherein at least one of said anesthetic absorber/desorber andsaid carbon dioxide retaining element is removably mounted in saiddelivery unit.
 8. An anesthetic inhalation system comprising: amechanical breathing assist device providing a supply of an inhalationgas; a gas flow circuit connected to said mechanical breathing assistdevice and adapted for connection to airways of a patient to transportsaid inhalation gas toward the patient and to transport exhalation gas,originating from the patient, away from the patient; and an anestheticsource for dosing said inhalation gas with an anesthetic agent, saidanesthetic supply comprising a delivery unit containing an anestheticabsorber/desorber and a carbon dioxide retaining element, an externallyaccessible first internal flow section in said delivery unit directinggas sequentially first through said anesthetic absorber/desorber andsubsequently through said carbon dioxide retaining element, and anexternally accessible second internal flow section in said delivery unitdirecting gas through said delivery unit through said anestheticabsorber/desorber and bypassing said carbon dioxide retaining element,said delivery unit being in gaseous communication with said gas flowcircuit said first internal flow section forming a flowpath for saidinhalation gas and said second internal flow section forming a flowpathfor said exhalation gas, and comprising a third internal flow section insaid delivery unit in gaseous communication with said first internalflow section and configured to provide a flowpath for only a portion ofgas from said first internal flow section to said carbon dioxideretaining element and said portion bypassing said anestheticabsorber/desorber.